Per Jon Peltier:
However, I always advise people to put the data into a worksheet range
somewhere and plot this range. It's easy to see the data and debug the
chart, and there are no arbitrary limits set in the days of limited hardware
capabilities.

That's what I wound up doing - and it's finally dawned on me that the user can
right-click the graph, select "Source Data", and Excel will take him right to
the range behind the chart.

Thanks for the alternative though.
--
PeteCresswell